Large neutrino mixing angle \theta_{13}^{MNS} and quark-lepton mass ratios in unified flavour models

Abstract

We analyse how a large value of the leptonic mixing angle \theta_{13}^{MNS} can be generated via charged lepton corrections in unified flavour models, using novel combinations of Clebsch-Gordan factors for obtaining viable quark-lepton mass ratios for the first two families. We discuss how these Clebsch-Gordan factors affect the relations between down-type quark mixing and charged lepton mixing in SU(5) GUTs and Pati-Salam unified models and calculate the resulting possible predictions for \theta_{13}^{MNS} for models with \theta_{13}^\nu, \theta_{13}^e << \theta_{12}^e. While symmetric mass matrices with zero (1,1)-elements always lead to comparatively small \theta_{13}^{MNS} \approx 2.8 degrees, we find novel combinations of Clebsch-Gordan factors for non-symmetric mass matrices which can yield \theta_{13}^{MNS} \approx 5.1 degrees, 6.1 degrees, 7.6 degrees or 10.1 degrees, as favoured by the current experimental hints for large \theta_{13}^{MNS}. We discuss applications to classes of models with underlying tri-bimaximal or bimaximal mixing in the neutrino sector.